A comparative study on the variability and trend in total ozone in the northern and southern hemispheres

249-255Using a statistical regression model, annual as well as seasonal trends in zonal mean total zone in the northern and the southern hemispheric latitudes have been studied. The study is based on total ozone data measured by total ozone mapping spectrometer (TOMS) from 1978 to 1991. In the present regression model, quasi-biennial oscillation (QBO) is removed from the data by selecting the period as 26 and 30 months respectively, depending on the strength of amplitude of QBO at higher and lower latitudes. The trend in global total ozone is found to be about -4% over the 13-year period. At higher latitudes of both hemispheres, significant decreasing trend is observed during all seasons. It is insignificant at 65°N during winter, with maximum decrease at 45°N. Near equatorial latitudes of the northern hemisphere showed a slight increasing trend and the negative trend extended to a broad area (45°-65°N) during spring. In the southern hemisphere, the depletion is found to be between 35° and 65°S from summer to autumn, and it is higher during summer compared to other seasons between 35° and 45°S